1. Field of Invention
The present invention relates to fracturing solid materials in general and to a method of fracturing rocks and concrete by containing an exothermic expansive reacting within a bore hole in particular.
2. Description of Related Art
It is often desirable to fracture or break large bodies of solid materials into more manageable sizes for transportation and further processing. Such solid material may be rock or concrete in the fields of mining, civil engineering or demolition work for example. Methods of fracturing such materials have typically been either mechanical or chemical.
Mechanical methods of rock breaking may include hammering or impacting the solid material, for example with a jack hammer. Mechanical methods may also include cutting or shearing, applying pressure by wedges as well as any means of applying a shock to the solid material. Chemical methods have typically relied on a chemical reaction within a cavity or bore of the solid material to produce a large amount of pressure within the bore. This pressure serves to fracture the solid material between the bore and a free surface. Chemical methods typically include the use of explosives for most large-scale operations. Chemical methods may also include the injection of an expanding foam into the bore holes or other suitable pressure producing methods.
The chemical methods of fracturing solid materials are typically preferred for a variety of reasons. Chemical methods, such as explosives, enable a large number of bore holes to be filled and exploded at the same time. This enables a large volume of solid material to be fractured at a single event. In addition, through timing of the explosions successively within an array of bore holes, the volume of solid material fractured may be further multiplied. The ability to fracture large volumes of material at a time leads to significant efficiency advantages. Efficiency in blasting operations is typically measured in terms of the amount of labor, equipment and materials required to break a volume of material. Explosive techniques tend to be efficient due to the ability to bore a large number of bore holes which may be fractured during a single event.
The use of explosives however has a number of disadvantages, many of which primarily result from the speed of the chemical reaction within the explosive material. As the explosive reaction is completed during a period of several milliseconds, the material surrounding the bore hole does not have sufficient time to expand, resulting in shattering of the material followed by displacement. This shattering of the material results in pieces of solid material that are no longer attached to any surrounding material and are briefly subjected to the violent expulsive force of the explosion. Accompanying this reaction is therefore a large amount of noise, flying debris, ground and air vibration and possible toxic fumes from the explosives themselves.
In addition, the use of explosives also increases the hazards of the excavation due to any possible unexploded material. If such unexploded material is lodged in the surrounding unfractured rock, it may be subject to being ignited by subsequent drilling operations. In addition, any unexploded material entrained with the fractured material may cause damage or danger to workers during subsequent collection and processing of the material. It will also be appreciated that due to the hazardous nature of explosives, specialized personnel are required to handle, operate and oversee these operations.
Thermite is a known chemical composition consisting of a mixture of particles of a metal oxide, such as, for example, FeO, iron (II) oxide or ferrous oxide and a reactive metal, such as, for example, aluminum. Thermite is an exothermic reactive material that will chemically react with itself once initiated thereby producing aluminum oxide and free elemental iron, for example, as well as releasing a large amount of heat.
Thermite has been proposed for use in breaking or fracturing solid material in U.S. Pat. No. 5,773,750 to Jae et al. Jae et al. however applies thermite into a bore hole on the end of a rod or stinger. The stinger of Jae et al. includes electrodes which serve to initiate the reaction of the thermite. As Jae et al. applies the thermite to the end of a stinger, only a single bore hole may be fractured at a time. Accordingly, Jae et al. is not capable of fracturing a large volume of solid material during a single event, and does not therefore achieve the efficiency advantages of typical explosive methods.
What is desirable is a method of fracturing rock by pressure that is applicable to a plurality of bore holes simultaneously wherein the pressure is developed and applied slow enough so as to diminish flying debris, air blast, ground vibration and excessive noise.